In order to evaluate the oil and gas producing potential of geological formations, it is known to attach a formation testing tool to a drill stem and lower the same into an inclosed well bore. Packer elements, which are used to isolate the zone which is to be tested for its producing potential, are lowered into the bore hole in a deflated state. When the formation testing tool attached to the drill stem is at the appropriate depth, the packers inflate on either side of the zone. After the test has been completed, the packers are deflated in order to permit the drill stem to be moved again.
Various inflatable packer systems have been proposed for use with drill stem testers. Some systems make use of the drill pipe rotation to actuate a piston pump which displaces fluid into the packer elements; in other systems, the drill pipe reciprocation actuates the piston pump to displace the fluid into the packer elements. The set-down movement of the drill pipe can also be used to move a piston to displace fluid into the packer elements. In still other systems, the drill pipe rotation or weight set-down opens a valve allowing compressed gas from a tank to move a piston so as to displace fluid into the packer elements.
Canadian Pat. No. 1,142,848 discloses one inflatable packer system which has been used in drill stem testing in the Canadian west. The system disclosed in the patent uses a rotary pump, actuated by rotating the drill stem, to pump drilling mud to the packer elements. A check relief valve is provided to guard against packer deflation in case of a loss of pump pressure, and against over-inflation and rupture of the packer elements. The valve subassembly incorporates a shifting sleeve which is pumped down upon initial operation of the pump. Pumping down the shifting sleeve opens a passage between the pump outlet and the packer elements so as to permit inflation of the packer elements.
When the packer system is inflated, weight is set-down on the drill stem to collapse the inner portion of the valve with respect to the outer portion of the valve. Initial movement of the inner portion of the valve isolates and seals off the packer elements; further movement vents inflation fluid from the pump to the well. Packer deflation is accomplished by lifting the drill stem to stretch the valve to its original elongated position. Initial lifting of the inner portion of the valve opens the vent to the well bore from the isolated zone to equalize the pressure in the zone with that in the well bore; further lifting causes the shifting sleeve to be picked up and opens a passage to the well bore from the interior of the packer elements, for deflation thereof.
In the operation of this prior art system, a mechanical latch must be released by pressure from the rotary pump in order to inflate the packer elements. This is a potential area of difficulty, where wearing or jamming may occur. Furthermore, in order to open a path for pressure fluid between the formation and the surfaee, the formation flow ports in the tool must move to open up relief ports between the pump and the release mechanism; the port is opened to the well bore after a short movement of the tool, so as to relieve any excess pressure, and then the port is resealed before the main valve opens. This design requires that the pressure between the pump and the release system be relieved, thus necessitating additional features. Finally, to release the packer elements, the ports must be aligned; again, the need to perform a mechanical latching operation presents an area vulnerable to wear and failure.